Preparation

Whisk 1 tablespoon oil, vinegar and both mustards in medium bowl to blend. Whisk in mayonnaise, then cream. Mix in 2 tablespoons chives. Season vinaigrette to taste with salt and pepper.

Cook potatoes in large saucepan of boiling salted water until just tender, about 12 minutes. Drain potatoes; pat dry with paper towels. Cool completely. Cut each potato crosswise into 4 slices.

Heat remaining 2 tablespoons oil in heavy large skillet over high heat. Add potatoes and sauté until golden, about 2 minutes per side. Using slotted spoon, transfer potatoes to plate. Add scallops to same skillet and sauté until just cooked through, about 1 minute per side.

Toss mixed greens in large bowl with enough vinaigrette to coat. Season salad to taste with salt and pepper. Spoon salad onto center of plates. Arrange scallops and potatoes atop salad. Drizzle remaining vinaigrette around scallops and potatoes. Sprinkle with additional chopped chives and serve.